Perimeter leakage current in polymer light emitting diodes Germa ` Garcia-Belmonte a, * , Jose ´ M. Montero a , Yassid Ayyad-Limonge a , Eva M. Barea a , Juan Bisquert a , Henk J. Bolink b a Departament de Fı ´sica, Universitat Jaume I, E-12071 Castello ´ , Spain b Institut de Cie `ncia Molecular-Universitat de Vale `ncia, Polı ´gon La Coma s/n, E-46980 Paterna, Vale `ncia, Spain Received 11 January 2008; received in revised form 14 March 2008; accepted 27 March 2008 Available online 15 April 2008 Abstract Observation of leakage current paths through the device perimeter in standard poly(phenylene vinylene)-based light-emitting devices is reported. Perimeter leakage currents govern the diode performance in reverse and low positive bias and exhibit an ohmic character. Current density correlates with the perimeter-to-area ratio thus indicating that leakage currents are mainly confined on polymer regions in the vicinity of metallic contact limits (device perimeter). Ó 2008 Elsevier B.V. All rights reserved. PACS: 73.61.Ph; 81.05.kf Keywords: Leakage currents; Edge shunt; Light emitting diodes 1. Introduction Organic light-emitting diodes (OLEDs) have attracted much attention because of their potential applications in flat panel and flexible displays, data communication, and lighting systems. Among other technological requirements, taking control over diode leakage currents is one of the determining aspects of the device performance. From a portable system designer’s point of view, leakage current may have dramatic negative effect on the standby life of the battery-powered device. Therefore, the physical origin of leakage currents in OLEDs should deserve much atten- tion for reliable device engineering. There are some indica- tions which relate the surface roughness of indium tin oxide substrates to the device leakage paths [1]. It is also believed that local damage of the organic layer induced during radio frequency or dc cathode sputtering lies behind the conduct- ing paths [2], and modifications of the deposition tech- niques have been proposed to avoid such problem [3]. The measured current–voltage (J–V) characteristics in polymer and small-molecule light-emitting devices (OLED) in reverse and forward bias direction up to approximately the built-in potential V BI often exhibits ohmic response. This behavior is believed to be caused by additional leak- age currents flowing in parallel with useful currents respon- sible for the device operation, J tot = J oper + J leakage . For voltages more positive than V BI a current increase starts indicating the potential-driven enhancement in charge car- rier injection. The existence of leakage currents governing the diode performance in reverse and low positive bias is well-known in inorganic electronics [4]. These effects are usually assimilated into a ‘‘shunt resistance” which accounts for the deviations from the ideal diode response. Such shunt resistance might be originated either by bulk processes or edge leakage paths. Apart from the impor- tance of regarding leakage currents in complete device modeling [5], practical applications of light-emitting diodes and other types of organic devices should take into account the influence leakage current might have on the overall sys- tem performance. For instance, operating currents involved in small-area devices (100–300 lm diameter), like 1567-1739/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2008.03.018 * Corresponding author. Tel.: +34 964 728040; fax: +34 963 729218. E-mail address: garciag@uji.es (G. Garcia-Belmonte). www.elsevier.com/locate/cap www.kps.or.kr Available online at www.sciencedirect.com Current Applied Physics 9 (2009) 414–416